<template lang="html">
 <div class="yo-scroll"
 :class="{'down':(state===0),'up':(state==1),refresh:(state===2),touch:touching}"
 @touchstart="touchStart($event)"
 @touchmove="touchMove($event)"
 @touchend="touchEnd($event)"
 @scroll="(onInfinite || infiniteLoading) ? onScroll($event) : undefined">
  <section class="inner" :style="{ transform: 'translate3d(0, ' + top + 'px, 0)' }">
   <header class="pull-refresh">
    <slot name="pull-refresh">
      <span class="down-tip">下拉更新</span>
      <span class="up-tip">松开更新</span>
      <span class="refresh-tip">更新中</span>
    </slot>
   </header>
   <slot></slot>
   <footer class="load-more">
    <slot name="load-more">
     <span>加载中……</span>
    </slot>
   </footer>
  </section>
 </div>
</template>
 
<script>
export default {
 props: {
  offset: {
   type: Number,
   default: 40
  },
  enableInfinite: {
   type: Boolean,
   default: true
  },
  enableRefresh: {
   type: Boolean,
   default: true
  },
  onRefresh: {
   type: Function,
   default: undefined,
   required: false
  },
  onInfinite: {
   type: Function,
   default: undefined,
   require: false
  }
 },
 data() {
  return {
   top: 0,
   state: 0,
   startY: 0,
   touching: false,
   infiniteLoading: false
  }
 },
 methods: {
  touchStart(e) {
   this.startY = e.targetTouches[0].pageY
   this.startScroll = this.$el.scrollTop || 0
   this.touching = true
  },
  touchMove(e) {
   if (!this.enableRefresh || this.$el.scrollTop > 0 || !this.touching) {
    return
   }
   let diff = e.targetTouches[0].pageY - this.startY - this.startScroll
   if (diff > 0) e.preventDefault()
   this.top = Math.pow(diff, 0.8) + (this.state === 2 ? this.offset : 0)
 
   if (this.state === 2) { // in refreshing
    return
   }
   if (this.top >= this.offset) {
    this.state = 1
   } else {
    this.state = 0
   }
  },
  touchEnd(e) {
   if (!this.enableRefresh) return
   this.touching = false
   if (this.state === 2) { // in refreshing
    this.state = 2
    this.top = this.offset
    return
   }
   if (this.top >= this.offset) { // do refresh
    this.refresh()
   } else { // cancel refresh
    this.state = 0
    this.top = 0
   }
  },
  refresh() {
   this.state = 2
   this.top = this.offset
   this.onRefresh(this.refreshDone)
  },
  refreshDone() {
   this.state = 0
   this.top = 0
  },
 
  infinite() {
   this.infiniteLoading = true
   this.onInfinite(this.infiniteDone)
  },
 
  infiniteDone() {
   this.infiniteLoading = false
  },
 
  onScroll(e) {
   if (!this.enableInfinite || this.infiniteLoading) {
    return
   }
   let outerHeight = this.$el.clientHeight
   let innerHeight = this.$el.querySelector('.inner').clientHeight
   let scrollTop = this.$el.scrollTop
   let ptrHeight = this.onRefresh ? this.$el.querySelector('.pull-refresh').clientHeight : 0
   let infiniteHeight = this.$el.querySelector('.load-more').clientHeight
   let bottom = innerHeight - outerHeight - scrollTop - ptrHeight
   if (bottom < infiniteHeight) this.infinite()
  }
 }
}
</script>
<style>
.yo-scroll {
 position: absolute;
 top: 2.5rem;
 right: 0;
 bottom: 0;
 left: 0;
 overflow: auto;
 -webkit-overflow-scrolling: touch;
 background-color: #ddd
}
.yo-scroll .inner {
 position: absolute;
 top: -2rem;
 width: 100%;
 transition-duration: 300ms;
}
.yo-scroll .pull-refresh {
 position: relative;
 left: 0;
 top: 0;
 width: 100%;
 height: 2rem;
 display: flex;
 align-items: center;
 justify-content: center;
}
.yo-scroll.touch .inner {
 transition-duration: 0ms;
}
.yo-scroll.down .down-tip {
 display: block;
}
.yo-scroll.up .up-tip {
 display: block;
}
.yo-scroll.refresh .refresh-tip {
 display: block;
}
.yo-scroll .down-tip,
.yo-scroll .refresh-tip,
.yo-scroll .up-tip {
 display: none;
}
.yo-scroll .load-more {
 height: 3rem;
 display: flex;
 align-items: center;
 justify-content: center;
} 
</style>